The Hilton San Francisco Union Square is a skyscraper hotel located several blocks south-west of Union Square in San Francisco, California. Opened in 1964, the innovative 18-story, 1200-room original building was known as a "motel within a hotel", allowing guests to park directly next to their upper-story rooms. Filling an entire city block, it remains one of the tallest structures representing Brutalist architecture, though it has been extensively altered since its construction. A second 46-story tower was added in 1971, while a third smaller 23-story connecting tower was completed in 1987. Renovated in 2017 and still operated by Hilton, it is currently the largest hotel on the West Coast, with 1,921 rooms.